A British hacker who broke into U.S. government computer systems seeking evidence of alien life has failed in his latest efforts to block extradition to the U.S. to face trial.

On Friday, the High Court ruled the extradition of Gary McKinnon, whose hacking exploits have drawn high-profile attention from U.K. Prime Minister Gordon Brown and celebrities such as David Gilmour of Pink Floyd, should proceed. Karen Todner, McKinnon's attorney, said they will lodge an appeal within 28 days, possibly taking the case to the U.K.'s Supreme Court.

McKinnon's attorneys had asked the court to review a refusal by the Director of Public Prosecutions (DPP) for England and Wales to prosecute the him in the U.K. British prosecutors maintain that the U.S. wants jurisdiction and that most evidence and witnesses are in the U.S.

McKinnon had also asked the court to review his extradition order, which was approved by the U.K. government in July 2006, on the basis of his diagnosis with Asperger Syndrome, a neurological disorder characterized by obsessive behavior and deficiencies in social interaction.

"Gary is clearly someone who is not equipped to deal with the American penal system, and there is clear evidence that he will suffer a mental breakdown if extradited," Todner said in a news release.

Todner said that on Friday she sent a letter signed by 40 Members of Parliament to U.S. President Barack Obama, asking him "to step in and bring this shameful episode to an end."

McKinnon faces up to 60 years in prison for hacking into 97 U.S. military and NASA computers between February 2001 and March 2002. He was indicted in 2002 in the U.S. District Court for the Eastern District of Virginia.

While in the U.K., McKinnon has freely admitted to hacking the computers using a program called "RemotelyAnywhere," a remote access tool. He has said that many of the computer systems still had their default passwords, which is generally considered a poor security practice, and that other passwords were easy to obtain.

McKinnon contends he didn't harm the computer but was merely searching for proof of the existence UFOs. The U.S. military contends that McKinnon deleted critical files from its computers, which hampered its efforts after the Sept. 11, 2001, terrorist attacks.